A small anemometer with flat vanes which indicates the number of linear feet or meters of air which have passed the instrument during its exposure.

General term for any device that measures precipitation: principally a rain gauge or snow gauge.

United Kingdom forecast model. (Available via AccuWeather.com Professional.)

Forecasting weather by the use of numerical models, run on high speed computers. Most of the NWP for the National Weather Service is done at the National Centers for Environmental Prediction (NCEP).

For a given cloud or cloud laver. the lowest level in the atmosphere at which the air contains a perceptible quantity of cloud particles.

Any one of numerous devices for the measurement of either speed alone or of both direction and speed (set and drift) in flowing water.

See evaporative opportunity.

A unit of luminance or brightness equal to 1/d candles per foot'.

A wind blowing in a direction perpendicular to the course of a moving object.

Movernent of water through the soil surface into the soil, or the quantity of water entering the soil. Infiltration is equal to the total precipitation less the losses due to interception by vegetation. retention in depressions on the land surface, evapor ...

An instrument for measuring the intensity of light or the relative intensity of a pair of lights. Also called an illuminometer. If the instrument is designed to measure the intensity of light as a function of wavelength, it is called a spectrophotometer. ...

Based upon damage patterns, classifies twisters into six categories of wind speed (F0 thru F5), ranging from 40 to 318 mph estimated wind speed.

A psychrometer in which the ventilation is provided by a suction fan.

The outer, solid portion of the earth: the crust of the earth.

A system of physical units based upon the use of the meter, the metric ton (106 grams), and the second as elementary quantities of length, mass, and time, respectively.

An instrument for measuring the extinction coefficient in water.

The officially designated elevation of an airport above mean sea level, taken as the highest point on any of the runways of the airport. Same as airport elevation.

Pyrheliometer based on the comparison of the heating of two identical metal strips, one exposed to radiation, the other to a joule effect.

An instrument whose calibration can be determined by means of simple physical measurements on the instrument. Compare to secondary instrument.

The ceiling classification which is applied when the ceiling height is determined by timing the ascent and disappearance of a ceiling balloon or pilot balloon.